Synthetic linear polyamides containing intralinear siloxane groups and preparation



United States Patent SYNTHETIC LINEAR POLYAMIDES CONTAINING SILOXANE GROUPS AND PREP- ARA 0 Stanley Brooke Speck, Buffalo, N. Y., assignor to E. I. du Pont de N emours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 31, 1951, Serial No. 208,843

13 Claims. (Cl. 260-465) This invention relates to polymeric materials and more particularly to newfiberand film-forming synthetic linear condensation polymers having new and unusual properties.

This application is a continuation-in-part of my copending application Serial No. 106,322, filed July 22, 1949.

It is known to react difunctional reactants capable of yielding linear condensation polymers, under conditions such that linear condensation superpolymers are formed which can be spun into useful filaments capable of being cold drawn. Carothers U. S. Patents 2,071,250, 2,071,- 253, 2,130,523 and 2,130,948 in particular, disclose the preparation of such linear condensation superpolymers. Those polyesters and polyamides described in the aforementioned patents having an intrinsic viscosity greater than 0.3 are primarily useful as fiber forming materials, and because of their stability, high melting points, relative insolubility, etc., they are very useful in the textile and allied arts. The lower molecular weight linear condensation polymers are used with great advantages in coating compositions, and as softeners, moulding powders, etc.

An object of this invention is to provide novel superpolymers of the class of linear condensation polymers.

Another object is to provide novel linear condensation superpolymers capable of being converted into colddrawable filaments having unusual and advantageous characteristics.

Still another object is to provide oriented filaments of novel linear condensation superpolymers, which filaments have good stability, strength, dyeing characteristics, elastic recovery, and an exceptionally high work recovery.

-A further object is to provide new and highly useful fiberand film-forming polyamides. The foregoing and other objects will more clearly appear hereinafter.

These objects are accomplished by heating to reaction temperature difunctional reactants capable of yielding linear condensation superpolymers, e. g., a diprimary, disecondary or primary-secondary diamine and a dicarboxylic acid or an amide-forming derivative thereof, at least one of said reactants containing silicon present in the reactant or reactants as a part of the divalent radical wherein R, R R and R are any monovalen-t hydrocarbon radicals, R is any divalent hydrocarbon radical from the group consisting of divalent aromatic and cycloaliphatic hydrocarbon radicals, and n is a number from 0 to 5 inclusive, the radicals R being attached to the amideforming functional groups (e. g. carboxyl and/or amino groups) of the difunctional reactant, and continuing the reaction until a polymer having the desired intrinsic viscosity is obtained.

The general process of formation of the various siliconcontaining intermediates involved for the preparation of this new series of silicon-containing polymers is illustrated in the following reactions. While thisseries of reactions 2,754,284 Patented July 10, 1956 components or amide-forming derivative or properties.

2. Condensation of a dibasic acid or amide-forming derivative thereof with a diamine.

While for maximum silicon content of the final polymer it is preferred to use reactants both of which contain the silicon atom (a self-condensing, silicon-containing material, i. e., acid, is comprehended, of course), it is obviously possible to reduce the silicon content in half by using one difunctional reactant containing no siliccon, e. g., hexamethylenediamine.

From the above it is apparent that all of the difunctional reactants described by Carot'hers as being useful in the preparation of polyamides may be used in connection with. one or more of the silicon-containing difunctional reactants described herein to form the new polymers of this invention.

In the preferred practice of the invention, the difunctional reactants are heated at polymer-forming temperatures, generally in the range of 180-300 C., in the presence or obsence of a diluent until the product has a sufiiciently high molecular weight to exhibit fiber-forming properties; As in the case of the conventional polyamides, the fiber-forming stage can be tested by touching the molten polymer with a rod and drawing the rod away. When this stage has been reached, a continuous filament of considerable strength and pliability is readily formed. With the polymers of this invention, this stage is generally the point at which the polyamide has an intrinsic viscosity of at least 0.4. Intrinsic viscosity is defined as:

Limit as C approaches wherein (117) is the viscosity of a dilute solution of the polymer in meta-cresol divided by the viscosity of metacresol in the same unit at the same temperature and C is the concentration in grams of the polymer for 100 cc. of solution. In general, measurement of the intrinsic viscosity is the most convenient method for following the course of the reaction and determining whether or not a fiber-forming product has been obtained. 7

The reaction by which these silicon-containing polymers may be obtained, is, as indicated above, a linear condensation polymerization. 7 It involves the formation of a by-product, such as water, alcohol, phenol, hydrogen chloride, ammonia, etc., depending upon the derivatives of the dibasic acid used in the reaction.

In general, the polyamides may be prepared most economically from a diamine and a dicarboxylic acid. The first reaction which occurs when the diamine and dicarboxylic acid are mixed and brought into sufiiciently initimate contact is the formation of the .diamine-dicarboxylic acid salts, The salt is generally crystalline and readily purified by recrystallization from a suitable solvent and is generally the starting material for the subsequent polymerization;

The conversion of the diamine-dibasic acid salt to a synthetic linear polymer is carried out by heating at polymer-forming temperatures, generally between l80300 C., in the presence or'absence of a diluent andunder conditions which will permit the by-product of the reaction to escape until an examination of a test portion of the product indicates it' has the desired fiber-forming As examples of diluents which may be used in the reaction may be mentioned phenol, cresols, xylenols, diphenylolpropanes and ortho-hydroxy diphenyl. White medicinal oil'is an example of a non-solvent which may be used. The first'stage of the reaction can be carried out in the presence of the condensation by-product, e. g., in an autoclave under pressure. or again, if the melt polymerization process is not desired, the polymer 'may be prepared by the solid polymerization process described in U. S. 2,172,374F1ory. H

The polymerization reaction may be carried out at atmospheric, super-atmospheric or sub-atmospheric pressure depending upon the best conditions suitable for the polymer and method of polymerization involved. The last stages of the reaction, at least, should be carried out under conditions which permit the escape of the byproduct of the reaction Unless this is water, a vacuum will generally be desirable. Preferably also, the reaction should be carried out in the absence of oxygen, e. g.; an atmosphere of nitrogen or in a vacuum. While it is generally unnecessary to add a catalyst, inorganic materials of alkaline reaction, such as oxides and carbonates, and acidic materials such as halogen salts of polyvalent elements, e. g. aluminum, tin are often helpful. Two examples of specific catalysts that may be mentioned are zinc borate and litharge. i

The polymers of this invention having an intrinsic viscosity of at least 0.4 are characterized by their fiberforming properties, i. e., their'ability to be formed into filaments which can be cold drawn to fibers showing by characteristic X-ray diffraction patternsorientation along the fiber axis. One method (wet process) of spinning these polymers into filaments consists of dissolving them in a suitable solvent and extruding the solution through orifices into a liquid which dissolves the solvent but not the polymer, e. g., a hydrocarbon or in some instances water, and collecting the filaments thus formed on a suitable revolving drum. Another method (dry process) consists in extruding the solution of the polymer into a heated chamber where the solvent is removed by evaporation. Still another method (melt process) consists in extruding the molten polymer through orifices into the atmosphere where it congeals into a filament. In some cases, particularly when the filaments are large, e. g., of bristle size, it may be advantageous to spin the' molten material into a cooling liquid, e. g., water. By similar processes the polymers can be formed into rods, sheets,

foils, ribbons, films and the like. In the various methods of formingshaped articles from products of this invention, particularly when these articles are obtained from solution, characteristics of the filaments, etc., can be altered by blending the polymers with other polyamides and polyesters and/or resins, plasticizers, cellulose derivatives, pigments, dyes, delustrants, etc.

After spinning, the filaments are normally cold drawn since this improves their strength and elasticity. The filaments from the products of this invention vary in the extent to which they can be cold drawn, but generally the degree of cold drawing possible-will lie between -500%. Although ribbons, sheets and the like can also be cold drawn, it is generally more advantageous to cold roll these products. By cold rolling such products in mutually perpendicular directions, it is possible to obtain products of great strength in all the directions.

Although the properties of the fibers formed from the polymers of this invention vary somewhat with the nature of the reactants used in the preparation, properties which characterize the fibers are super work recovery, good initial tensile modulus, elastic recovery, orientation along the fiber axis, as well as good strength and dyeing characteristics. a

Work recovery (WR) which is a criterion of resilience, is the ratio of the amount of work done by a yarn in recovering from. deformation to the work done in deforming it. To determine work recovery a stress-strain curve is used (plotting tension as the vertical axis vs. elongation as the horizontal axis) in which the yarn is extended at a constant rate of elongation of 1% per minute. The yarn specimen is held at the maximum elongation desired for 30 seconds and then allowed to retract at the same rate at which it was extended. The same specimen is extended successively severalditferent amounts. The areas under the elongation curve and the retraction curve, respectively,'represent work performed -on the material and work returned. These areas may Area (Work Returned) Area (Work Performed) Since the quantity of interest is a ratio, the absolute values of the work terms are not necessary.

Initial tensile modulus, which is also a criterion of resilience, is defined as the slope of the first reasonably straight portion of a stress-strain curve of the yarn obtained by plotting tension as the vertical axis vs. elongation as the horizontal axis as the yarn is being elongated at the rate of per minute. In almost every instance this is also the steepest slope to be found on the curve. The values as used herein are in units of grams per denier (g. p. d.) per 100% elongation.

The preparations of typical silicon-containing difunctional intermediates in accordance with the general reactions hereinabove set forth are illustrated by the following examples.

EXAMPLE A 1,3-bz's (p-carboxyphenyl) tetramethyldisilojcane a. p-TOLYLDIMETHYLCHLOROSILANE A solution of 720 parts of p-bromotoluene in 210 parts of absolute ether was added slowly to a mixture of 107 parts of magnesium, 560 parts of dimethyldichlorosilanc, and 910 parts of absolute ether under anhydrous conditions. The reaction was initiated by adding a crystal of iodine. The p-bromotoluene was added at such a rate as to maintain gentle refluxing of the mixture. After complete addition, the mixture was heated at the reflux on a steam bath overnight. The mixture was then filtered using a sintered glass filter and the filtrate distilled. Redistillation of a fraction boiling at 220-255 pure product boiling at 215-217 C., N. E., 179.6 (calculated, 184.5). The yield was about 50%.

b. 1,3-BIS (PJ TOLYL) TETRAMETHYLDISILOXANE This material was prepared by the hydrolysis and concurrent dehydration of p-tolyldimethylchlorosilane. The tolyldimethylchlorosilane, 250 parts wasplaced in a separatory funnel with 700 parts of ether and was. shaken with successive portions of cold water until the water was no longer acidic. The other layer was then dried over Drierite and the ether removed. The liquid residue was distilled and a yield of 157 parts (74%) of a clear, colorless liquid, B. P., 139l4l C. (0.2 mm.), was obtained. Since a benzene solution of this material did not react with sodium metal, the substance was assumed to be the disiloxane and not the silanol.

0. OXIDATION and reprecipitated with HCl. A yield of 54 parts (72%) of the acid, M. P., 220-230 C., N. E., 219, was obtained. In order to purify this crude acid, it was converted to the methyl ester which was purified and then hydrolyzed back of the acid. The ester was prepared by refluxing a mixture of 146 parts of the acid, 720 parts of methanol and 27.5 parts of concentrated sulfuric acid for14-5 hours. .The solution was then cooled, mixed with ether, and the solution washed several times with water, then with sodium bicarbonate solution. The ether layer'was'dried over Drierite and the ether distilled off. The residual gave a fairly 6 oil was crystallized from hexane yielding .parts of material, M. P., 5 8-62 C. Recrystallization from hexane gave 60'parts of ester, M. P., 57-61. The above ester was hydrolyzed by refluxing with 315 parts of ethyl alcohol and 17 parts of potassium hydroxide in 20 parts of water for 1-2 hours. The resulting solution was poured into cold water, washed with ether, treated with Darco and acidified with concentrated HCl. The acid after drying melted at 225234 C. and had a neutral equivalent of 191 (calcd., 187).

EXAMPLE B 1 ,7-bis(p-carboxyphenyl) -1,1,7,7-tetraphenyl-3,3,5,5- tetramethyltetrasiloxane A solution of 360 parts of p-bromotoluene in 250 parts of absolute ether was added slowly to a mixture of 506 parts of diphenyldichlorosilane and 55 parts of magnesium in 700 parts of absolute ether. The reaction was initiated by adding a crystal of iodine. After complete addition of the bromotoluene the mixture was heated at the reflux for 1% hours after which it was filtered in a dry box, the residue being washed thoroughly with dry benzene. The filtrate was then distilled and the fraction boiling at 175 205 C. (0.3 mm.) being collected as crude p-tolyldiphenylchlorosilane. This fraction was redistilled and that portion boiling at 175-185 C. (0.3 mm.) was collected. A yield of about 400 parts was obtained. This material was further purified by recrystallization from hexane.

The tolydiphenylchlorosilane was hydrolyzed by dissolving in ether and shaking in a separatory funnel with successive portions of cold water until the water was no longer acid to litmus. The ether layer was then dried and the ether removed at reduced pressure. The residue crystallized to a solid, melting point 78-85 C. and the silanol was purified by recrystallization from hexane.

The above compound was identified as a silanol by the fact that the benzene solution reacted with sodium and also because the materialcouldbe dehydrated to 1,3-dip-tolyltetraphenyldisiloxane.

l7. CONDENSATION OF p-TOLYLDIPHENYLSILANOL WVITH 1,3-DICHLOROTETRAMETHYLDISILOXANE A solution of 51 parts of the dichlorodisiloxane was added slowly and with constant stirring to a solution of 145 parts of the silanol and 60 parts of pyridine in 350 parts 'of dry benzene, maintaining the temperature at room temperature, by occasional cooling. Atfter complete addition, the mixture was heated at reflux for about 2 hours. It was then poured into water, ether added and the organic layer washed several times with water, after which it was dried over calcium chloride. The ether and benzene were then removed by warming on a steam bath at reduced pressure. The .residue was a viscous, colorless liquid amounting to 169 parts. It. finally crystallized to a rather waxy solid melting at 47-52" C. The material was oxidized directly to the acid without further purification.

e. OXIDATION OF THE1,7-DI-p-TOLYLTETRASILOXANE A solution of 169 parts of the tetrasiloxane in 510 parts of pyridine and '130 parts of water, was warmed on a steam bath and 320 parts of potassium permanganate added portion-wise over a period'of 1-2 hours while stirring vigorously. The resulting reaction'caused the mixture to reflux during this period; After'complete addition of the permanganate, parts more of water enamel wasv added and the mixture heated an additional 2 hours with stirring Methanol was then added to'destroy-the excess permanganate, and the mixture filtered, the residue being washed thoroughly with hot water.

The Colorless filtrate was made acid with concentrated HCland the mixture extracted with ether. The ether solution was washed with acidified water, dried and evaporated todryne'ss. The thick, colorless liquid Was stirred with500 parts of hexane causing a white solid to crystallize. A yield 'of 115 parts was obtained. After two recrystallizations from benzene-hexane (l to 2.5) the material melted at 117122 C., N. E., 415 (calculated, 383). Repeated recrystallizations of this material gave no further apparent purif cation. It was then found that,

after heating in a vacuum oven at 100 C. overnight, the material had a neutral equivalent of 389 and a melting point of ISO-152 C; The acid had originally crystallized as a partial hydrate. r

I EXAMPLE c Bis( p-aminomethylphenyl) dimethylsilane a. BIS -BROMOPHENYL) DIMETHYLSILANE residue was decomposed with water and the ether layer washed, dried and distilled. Appreciable quantities of bromobenzene and p-dibromobenzene were obtained in the forerun. A yield of 38 parts (31%) of a colorless oil, 'B. P. 155-170 C. (.2 mm.)'w'as obtained. After several recrystallizations from ethanol the compound was obtained as colorless needles, M. F. 72-73 C. Anal. calcd. for CriHmBrr'siz Br, 43.2. Found: Br, 41.3.

b. CONVERSION OF BIS (p-BROMOPHENYL) DIMETHYL- SILANE TO THE DINITBILE A mixture'of 14.8 parts (.04 mole) of bis(p-bromd phenyl) dimethylsilane, 8.5 parts of cuprous cyanide and parts of dry pyridine was sealed at atmospheric pressure in a tube and the tube heated at 250 C. for 3 /2 hours. During this period the contents were shaken several times. The dark colored liquid reaction mixture was cooled and then poured into ether. After stirring thoroughly for a few minutes the mixture was filtered and the "dark colored solid residue washed thoroughly with ether. The solid residue, 21 parts .when dried, .was thought to be a pyridine-cuprous cyanide complex.'

The ether solution was washed several times with concentrated ammonium hydroxide then with dilute HCl and finally dried and evaporated to dryness. The residual oil, 715 parts, was dissolved in 20 parts of ethyl alcohol, treated with Darco and allowed to crystallize. There was obtained 5 parts of light yellow crystals, M. P. 73-74 C. Several recrystallizations from 3:1 hexane-benzene mix- .ture gave colorless plates M. P. 100101 C.

.Anal.-Calcd. for C16H14N2Si: N, 10.70; 'Si, 10.71. Found: N, 10.84; Si. 10.87.

i c. BIS (p-AMINOh/IETHYLPHENYL) DIMETHYLSILANE was obtained. This materialhad a nitrogen content of 10.68% and a neutral equivalent of 135.5, theoretical being N=10.36% and N. E.=135.

The following examples are specifically illustrative of the preparation and application of the products of this invention from typical silicon-containing intermediates. Parts and percentages are by weight unless otherwise indicated.

' EXAMPLE 1 phenyl)tetramethyldisiloxane is prepared by adding an alcohol solution of hexamethylenediamine to a nearly equivalent quantity of the acid dissolved in alcohol. The precipitated salt is washed with alcohol and ether, then dried. This salt melts at 225-230. It is polymerized by heating for one hour at225 in a sealed evacuated tube followed by a one-hour heating cycle at 250 in an atmosphere of nitrogen. Polymerization is concluded by heating in high vacuum at 259 for 4 hours. The polymer is clear, colorless and can be manually spun into fibers or melt pressed into films. The intrinsic viscosity is .48 and the softening temperature is 140-145 EXAMPLE 11 The salt of bis(arn inomethylphenyl) dimethylsilane and bis(p-carboxyphenyl) tetramethyldisiloxane, M. P. 140, 7

mto mono-filaments which have the following properties:

Tenacity g. p. d 1.1 Elongation percent 7.6 Initial tensile modulus 30 Work recovery: Percent 1% elongation 99 2% elongation 97 3% elongation 92 EXAMPLE III The hexamethylene diamine salt of 1,7-bis(p-carboxyphenyl)1,1,7,7 tetraphenyl 3,3,5,5 tetramethyltelrasiloxane, melting point 205-210", is prepared in the manner previously described in 85% yield. The polymer is prepared by heating for hour at 218 in an atmosphere I of nitrogen followed by a one-hour cycle at 259 and concluded with one-hour cycle in high vacuum at 259. The

clear, colorless polymer has an intrinsic viscosity of .32

' and sticking'temperature of 140.

EXAMPLE IV 1,7 bis(p-carboxyphenyl)1,1,7,7 tetraphenyl 3,3,5,5- tetramethyltetrasiloxane, melting point 210215, is prepared in 90% yield. It is polymerized by the following heating cycle: 4 hour at 259 in an atmosphere of nitrogen; one hour at 259 in high vacuum and /2 hour at 273 in high vacuum. The polymer has an intrinsic viscosity of .3, softening temperature -155, and is clear andcolorless. 7

As many widely different embodiments can be made without departing from the spirit and scope of thisinvention, it is to be understood that said invention is in no way restricted save as set forth in the appended claims.

' V 1. A process for producing synthetic linear polyamides.

which comprises heating together as polyamide-forming reactants a diamineanda compound from the group con- 'sisting of dicarboxylic acid and amide-forming deriva- The hexamethylenediamine salt of 1,3-bis (p-carboxytives thereof, at least one of said reactants containing amide-forming functional groups of said,p.olyamide- Silicon present in the divalent radical forming reactants, and continuing the heating under con R3 ditions effective to remove volatile by-products of the reaction until a polymer having an intrinsic viscosity of I at least 0.4 is obtained. I 4 2 n 4 4. A synthetic linear polyamide containing the recurwherein R, R R and R are any monovalent hydro- 1mg structural ,5 i j carbon radicals, R is a divalent hydrocarbon radical 1'1 fl) 5H, (3H, o H selected from the group consisting of divalent aromatic H and cycloaliphatic hydrocarbon radicals, and n is a num- (C N C 0 1 g N her from 0 to 5 inclusive, the radicals R being attached H! to amide-forming functional groups of said polyamide- 5. A synthetic linear polyamide containing the recurforming reactants, and continuing the heating under ring structural unit:

1 CH; Iii 0 CH: OH: H CH:-i-CHgNi J- iO i lHs $113 6H3 conditions efiective to remove volatile by-products of the reaction until a polymer of the desired intrinsic viscosity 6. A synthetic linear polyamide containing the recuris obtained. v ring structural unit:

1? IOi CH: CH: O H (CHz)o-NC si01ii-oi-0-si- 3l I- O 47H: 41H: 0 2. A process for producing synthetic linear polyamides 7. A synthetic linear polyamide containing the recur- Which comprises heating together-as polyamide-forming ring structural unit:

OH: H O CH: CH; O H

reactants a diamine, and a dicarboxylic acid, at least one 5 8. A synthetic linear polyamide containing the recurof said reactants containing silicon present in the divalent ring structural unit:

radlcal R8 R1 R3 Z Y X Y wherein X has the structure:

1i! R R 50 R3 R1 R3 wherein R, R, R and R are any monovalent hydro- V I R di-(0 s'i 0-i. R carbon radicals, R is a divalent hydrocarbon radical n selected-from the group consisting of divalent aromatic and cycloaliphatic hydrocarbon radicals, and n is a numwherein R, R R and R are any monovalent hydrober from 0 to 5 inclusive, the radicals R being attachedsto carbon radical, R is a divalent hydrocarbon radical from amide-forming functional groups oftsaid p0lyamide-formthe group consisting of divalent aromatic and cycloaliing reactants, and continuing the heating under conditions phatic hydrocarbon radicals and n' is a number from 0 efiective to remove Volatile by-products of the reaction to 5; Y hasthe structure: until a polymer of the desired intrinsic viscosity is obtained. r J a V V 3; Aprocess'for producing synthetic linear polyamides CN which comprises heating together as polyamide-forming reactants a diamine, and a dicarboxylic acid, at least one and Z is a member of the group consisting of alkylene, of said reactants containing silicon present in the divalent 35 X and radical R1 R3 R1 R8 g R- si- O-S i O-i-R- 4 z 4 2 wherein R, R R and R are any monovalent hydru- 9. A synthetic linear polyamide containing the recurcarbon radicals, R is a divalent hydrocarbon radical ring structural unit: selected from the group consisting of divalent aromatic H O O H and cycloaliphatic hydrocarbon radicals, and n is a numu H l her from 0 to 5 inclusive, the radicals R being attached to ZN O X a 11 a a a p12,, wherein X has the structure: t V v wherein Y has the structure;

a a -31-- H --R---i--(O-i)O-S i-R l V I C N a r a and n is a number from 0 to 5. wherein R R, R and R are any monovalent hydro- 11. A synthettic linear polyamide containing the re carbon radical, R is a divalent hydrocarbon radical from curring structural unit:

y 7 wherein n is a number from 0 to 5. t 7 a the group consisting of divalent aromatic and cyclo- 12. A synthetic linear polyamide containing the re aliphatic hydrocarbon radicals and n is a number from curring structural unit:

CH; n

0 to 5, and Z is a member of the group consisting of wherein Y has the structure: alkylene, X and o H j '1 i R and n is a number from 0 to 5. r

R: 13. A synthetic linear polyamide containing the recurring structural unit:

* w cg igmiig tbfivggii 10. A syntheticlinear polyamide containing the rewherein n is a number from 0 to 5. curring structural unit: a a

References Cited in the file of this patent UNITED STATES PATENTS 7 0H: 1 2,130,948 Carothers Sept. 20, 1938 ,1k,,,,,e. YOi 0-8L O 10y. 2,386,452 F m 9, 1945 t 6 7 7 2,527,590 Speier Oct. 31, 1950 3 2,601,237 Barry et a1. June 24, 1952 2,618,646 Hatcher et a1. Nov. 18,1952

2,628,244 Speier Feb. 10, 1953 a 

1. A PROCESS FOR PRODUCING SYNTHETIC LINEAR POLYAMIDES WHICH COMPRISES HEATING TOGETHER AS POLYAMIDE-FORMING REACTANTS A DIAMINE AND A COMPOUND FROM THE GROUP CONSISTING OF DICARBOXYLIC ACID AND AMIDE-FORMING DERIVATIVES THEREOF, AT LEAST ONE OF SAID REACTANTS CONTAINING SILICON PRESENT IN THE DIVALENT RADICAL 